The present invention relates to particles which have been modified by a modifier and a dispersion comprising the modified particles.
Zinc oxide is a promising semiconductor in thin film transistors (TFTs) for producing advantageous TFT circuits in large displays or other electronic circuits.
A critical step in the production of these metal oxide semiconductor FETs (MOSFETs) is the deposition of zinc oxide or other semiconductors on the respective substrate.
There is great interest in depositing semiconductors on polymeric or other flexible substrates since these are advantageous not only in terms of their low weight and mechanical stability but can also be processed by significantly more advantageous deposition from dispersions by methods such as spin coating, dip coating or printing techniques. However, polymeric substrates limit the processing window to below 200° C.
A colloidally stable dispersion is important for the deposition in order to make formation of a homogeneous layer of finely divided nanosize particles possible. Additives (modifiers) which effectively prevent agglomeration of the primary particles are required for this purpose. The use of such additives in general has also been known for a long time from other applications.
WO 2006/138071 and WO 2006/138072 each disclose a process for the deposition of a semiconducting zinc oxide layer on a substrate from a colloidal dispersion. The dispersion is preferably applied at room temperature and subsequently baked at temperatures below 300° C. (annealing). The dispersions used are stabilized, but nothing is said about any stabilizers or modifiers.
DE 102 57 388 A1 describes a surface-modified nanoparticulate zinc oxide for use in cosmetic formulations, in which the surface modification comprises coating with an organic acid of the general formula HOOC—R1—(CH2)n—R2—CH3, where R1═CH2—(O—CH2—CH2)m; where m=0 to 11, n=0 to 30 and when m=0, n is greater than 11; and R2═CH2, CHCH2, C(CH3)2, phenylene, O, S. As preferred modifiers, mention is made of lauryl ether-11-polyethyleneglycolic acid, capryl ether-6-polyethyleneglycolic acid, lauryl ether-4-polyethyleneglycolic acid, lauryl ether-6-polyethyleneglycolic acid and/or lauryl ether-8-polyethyleneglycolic acid.
DE 10 2005 007 374 A1 discloses nanoparticles which have been modified by a biodegradable polymer, in particular polyesters, polycyanoacrylates, polyacrylates, polymethacrylates, polyepoxides, polyurethanes and polystyrenes. EP 1630136 A1 discloses titanium dioxide particles which have been modified by a hydrophilic polymer, in particular polycarboxylic acids. The carboxyl group of the modifier is bound via an ester bond to the titanium dioxide. Further modifiers are described in DE 10 2005 047 807 A1.
The modified particles or dispersions used hitherto have the disadvantage that they considerably worsen the performance of semiconductor components in the deposition of conductive, semiconducting or dielectric layers or it is necessary to employ a thermal treatment at temperatures at which the substrates are damaged in order to improve the performance. This is particularly true when using polymer substrates whose thermal stability is generally lower than that of inorganic substrates.
It is therefore an object of the invention to provide particles from which it is possible to produce a dispersion which is stable, can be processed readily and by means of which conductive, dielectric or semiconducting layers in semiconductor components which have only a low level of impurities, in particular impurities due to modifiers, can be produced.